Fluid pump with a rotor

ABSTRACT

The invention relates to a fluid pump, in particular to a liquid pump having a rotor ( 18 ) with at least one rotor blade ( 20, 21 ) for conveying the fluid, the rotor being variable with respect to its diameter between a first, compressed state and a second expanded state. In order to produce simple compressibility and expandibility of the rotor of the pump, it is provided according to the invention that at least one rotor blade is deformable between a first state which it assumes in the compressed state of the rotor and a second state which it assumes in the expanded state of the rotor by means of a fluid counterpressure ( 23 ) during a rotation of the rotor during pump operation.

The invention resides in the field of fluid pumps and relates to a pumpwhich is variable with respect to the rotor diameter thereof in order tobe able to be guided for example through narrow openings, such as tubes,in particular blood vessels, and to be able to be operated in theexpanded state after being guided through.

The invention can hence be provided, on the one hand, in the medicalfield, for example as blood pump for heart support, in a minimallyinvasive manner, however, on the other hand, use in agitators or as apropulsion element for ships is also conceivable.

The invention can exhibit particular advantages in the medical field asa result of possible miniaturisation.

After introducing the fluid pump through a large blood vessel into theventricle and subsequently setting it in operation after expansion ofthe rotor, the pumping power of a heart can be assisted thereconsiderably for example in humans or can be partially replaced. Thetherapeutic advantage of such applications resides in an at leastpartial relief of the heart muscle.

Expandable fluid pumps of this type are known from the state of the artalready. For example, a pump emerges from DE 10 059 714 C1 which can bepushed through a blood vessel together with the pump drive. The bloodflows there through a cannula, the diameter of which can be expanded andcompressed in order to change the flow ratios.

A blood pump, the rotor of which can be compressed and expandedradially, is known from WO 03/103745 A2, different constructions beingproposed there in order to achieve the expandability. For example bymeans of different mutually displaceable parts of the catheter afterintroduction, compressing of the pump housing and radial widening,associated therewith, can be effected. On the other hand, by rotating adrive shaft relative to a wire located in the catheter, the possibilityis disclosed of producing a helix structure of the wire, the wirecarrying in addition a membrane which forms a rotor blade after assumingthe helix structure.

In addition, a rotor structure having a plurality of blades which arerigid per se and articulated pivotably on a central part is known fromthe document, said blades being deployed during operation and henceproducing a fluid pressure.

A pump is known from EP 0 768 900 B1, in which rotor blades arearticulated on a shaft within a pump housing in such a manner that theycan be folded against the shaft in the inoperative state and, duringoperation, can be deployed perpendicular to the shaft in order to conveythe fluid.

From US 2006/0062672 A1, a rotor of a fluid pump is known with bladesthat are pliably fixed to a hub and that are deployed by the fluidcounterpressure generated by initial rotation of the rotor.

It is common to the known state of the art that rotor blades of a pumpare pivoted either by means of a pivot mechanism for expansion or byfluid counterpressure during rotation or are formed by a mechanicaldevice in the manner of a Bowden cable or the like only for expansion ofthe pump.

The object underlying the present invention with the background of thestate of the art is to produce a fluid pump having a rotor which can becompressed with respect to the diameter thereof, which is built assimply as possible constructionally, which preferably comprisesbiocompatible materials like the pump housing surrounding it, theexpansion and compression of which housing can be effected as simply aspossible and which has the necessary reliability during operation.

The object is achieved according to the invention by the features ofpatent claim 1.

In addition, the invention relates to methods for operating the fluidpump according to the invention according to claim 16, 17 or 18.

The knowledge underlying the invention is that as simple a structure aspossible of the fluid pump can be achieved by deformability of a rotorblade itself. The rotor of the fluid pump has, for this purpose, atleast one rotor blade which is located in a first state as long as therotor assumes a first, compressed state, the rotor blade assuming asecond state during transition of the rotor into an expanded state bymeans of deformation.

The rotor blade is thereby transferred from the first state into thesecond state by the fluid counterpressure which occurs during rotationof the rotor during the pump operation.

A particular advantage of the invention resides in the fact that noactuation elements require to be provided for expansion of the rotorapart from the actual drive of the pump and in the fact that, due to thedeformability of the rotor blade or blades per se, also no pivotablearticulation of rotor blades to other parts of the pump requires to beprovided.

The deformation of the blade is facilitated and at the same timedelimited by providing a leading and a trailing side of the blade in thedirection of movement during the conveying operation, wherein said sideshave different configurations in the form of different materialproperties and/or constructional assembly at least along a part of thedistance between the radially outer tip of the blade and the radiallyinner end of the blade.

The delimitation should thereby advantageously be, due to deformation,where a shape of the rotor which permits optimum conveying power isadopted. In other words, the deformability of the at least one rotorblade is advantageously delimited in such a manner that the deformationdoes not go beyond the shape in which the rotor produces the greatestpossible fluid counterpressure.

When the fluid pump is being guided through a tube, for example a bloodvessel, also no attempt is made by the rotor to expand without externalinfluences. Such an attempt would not be desirable in medical use sincethe walls of the blood vessels through which the pump is guided shouldnot be damaged. When applying through a tubular artificial access(valve), the described restoring forces would represent a particulardifficulty since, as a result, high frictional forces would be producedon the wall of the artificial tubes and significant forces would requireto be produced to feed the fluid pump into the interior of the body.

As long as the pump is not being operated, i.e. is not rotated on thepump shaft, the rotor remains in the compressed state and can be fedthrough the blood vessel.

If the pump is put in operation in situ, then the rotor is actuated inthe conveying direction and the rotor blade or blades are deformed bythe fluid counterpressure and hence deployed, as a result of which theactual, extensive conveyance is set in motion. It is therebyadvantageous if the deformation of the rotor blade/blades is elasticsince, in many application cases, the fluid pump must be compressedagain after application in order to be removed.

In this case, the rotor blade/blades assumes/assume their first stateagain, in which the rotor is compressed, after ceasing the pumpoperation and stopping the rotor.

Normally, the side of the rotor blade which is leading during operation(high pressure side) is predominantly subjected to tension whilst thetrailing side (suction side) is subjected to a compressive stress. Theinterface between the leading and the trailing sides can thereby beimagined as where a neutral load is present in the pump operation. Thisinterface must absorb corresponding transverse and shear stresses.

It can be provided for example that the leading side and the trailingside of the rotor blade are glued to each other in the region of theinterface or are connected to each other by other joining techniques.

The properties of the rotor blade which are advantageous for theinvention can be achieved for example in that the leading side of the atleast one rotor blade comprises a first material and the trailing sidecomprises a second material which is different from the first. The twomaterials may be both different plastic, for example polymers withdifferent properties, for example with different additives or one ofthem reinforced by fibers. It is also possible that one of thelayers—preferably on the trailing side—comprises an elastomer and theother layer a polymer. The rotor blade also could be made of severalthin layers of plastic material wherein each layer has differentproperties, e.g. a first layer with a low parameter, a second layer witha parameter higher than the first, a third layer with a parameter higherthan the second layer etc. (the parameter may be any mechanical propertyor the like). If these layers are thin enough, the change of parameterover the thickness of the blade is (at least on a macroscopic scale)continuous. Such a plurality of layers may be manufactured by sprayingand/or sputtering etc. of different materials for each layer.

It proves to be advantageous if the first material is more ductile thanthe second material.

The first material should thereby have a permanent elongation limit sothat, during deformation of the rotor blade, a limit which is asprecisely defined as possible is achieved during the pump operation anda defined shape of the rotor blade is set during operation. Such apermanent elongation limit is provided for example by a non-linear rangeof the coefficients of elasticity of the material so that the forcerequired for elongation increases superproportionally from a specificpermanent elongation limit and the shape is stabilised as a result. Thisproperty can be intrinsic to the first material but it can be assistedor essentially produced in that stretch-resistant fibres are embedded inthe first material, said fibres being substantially morestretch-resistant than the first material itself and being presentunstretched in the first state of the rotor blade and in stretched formin the second state in the first material. Such fibres can be formed forexample by high-strength plastic materials or by glass or by carbonfibres.

The second material on the trailing side of the rotor blades can beincompressible or be deformable only up to a specific compressibilitylimit. The deformability is advantageously elastic. The compressionlimit can be formed for example by a non-linearity of the compressioncoefficients in that the force required for the compression risessuperproportionally from a specific compression degree.

It may also be advantageous if a first layer of material on the leadingside and a second layer of material on the trailing side are providedwherein the second layer comprises trenches that allow for compressionof said second layer up to the extent that the trenches are closed.

The trenches may be tangential to a circumferential direction of therotor in order to allow for a bending of the rotor blade(s) along theirradial length.

It can also be provided advantageously that the at least one rotor bladehas, on the trailing side, shaped elements which are at a spacing fromeach other in the first state and abut against each other in the secondstate.

These shaped elements can be separated from each other in the firststate by slots or also be embedded in a compressible material. At anyrate they delimit further deformability of the rotor blade in that theyabut against each other in the second state.

A further advantageous embodiment of the invention provides that atleast one stop element is mounted on one side of the at least one rotorblade, said stop element penetrating the interface between the leadingside and the trailing side and being moveable in a limited manner in arecess on the other side of the rotor blade.

The stop element is advantageously produced from a material which isvirtually as incompressible or precisely as incompressible as thematerial which the trailing side of the rotor blade comprises in orderto achieve a defined stop position. The stop element can comprise forexample a metal or a hard plastic material.

The invention relates, apart from to a fluid pump, in addition to amethod for operating a fluid pump of the described form, the pump beingstarted by rotation of the rotor in the operating direction and therotor being expanded by the fluid counterpressure.

It can also be provided in addition that, in order to reduce the rotordiameter, the rotor is actuated in the direction opposite to theoperating direction.

It is hence made possible by the invention that, when the pump is guidedthrough an opening, in particular a blood vessel, the rotor is actuatedin the direction opposite to the operating direction and hence iscompressed.

The invention may also comprise that at least one rotor blade comprisesat least one winglet for optimizing the fluidic conditions (see FIGS.13/14 in which “W” denotes a winglet and “B” denotes a blade). FIG. 15shows an alternative embodiment with a winglet W′ which is only on theleading side of the blade B′.

It may be advantageous that the at least one winglet protrudes from theleading side and/or from the trailing side of the blade.

The fluidic conditions between the rotor and the inner wall of a pumphousing are best optimized by that at least one winglet is positioned atthe tip of the blade. This winglet may also provide a bearing for therotor insofar as it is gliding at the inner wall of the pump housing.However, winglets may also be provided between the tip and the radiallyinner end of a blade where they can influence the fluid flow.

The winglets may be fixed pivotable with regard to the blade and maybeeasily pivoted into their operating position by fluid pressure that isgenerated when the rotor is rotating (see FIGS. 14 and 15).

The current invention also refers to a method for making a fluid pump asit has been described above.

The invention is illustrated subsequently in a drawing with reference toan embodiment and is explained subsequently.

There are thereby shown:

FIG. 1 schematically, the application of a fluid pump in a heart forconveying blood,

FIG. 2 schematically, a pump head in longitudinal section with radialinflow,

FIG. 2 a schematically, a pump head in longitudinal section with axialinflow,

FIG. 3 schematically, a rotor with two rotor blades in a plan view,

FIG. 4 a rotor in a lateral view,

FIG. 5 a section through a part of a rotor blade,

FIG. 6 a section through a part of a rotor blade in a differentembodiment,

FIG. 7 a section through a part of a rotor blade,

FIG. 8 a sectional enlargement of the detail described in FIG. 7 withVIII,

FIG. 9 a section through a rotor blade in a further embodiment,

FIG. 10 an embodiment of a rotor with a helical rotor blade which issupported by shaped elements,

FIG. 11 a rotor, the helical blade of which is supported by a spiralwinding,

FIG. 12 a rotor, the helical rotor blade of which is supported by aconnecting member guide,

FIG. 13 a perspective view of a blade with a winglet,

FIG. 14 a sectional view of the device of FIG. 13,

FIG. 15 a sectional view of an alternative design of a blade/winglet.

FIG. 1 shows schematically in cross-section a heart 1, in which the head3 of a fluid pump protrudes into a ventricle 2. The pump head 3 isdisposed at the end of a cannula 4 and has a pump housing 5 which isrounded at the front.

The drive of the pump is effected via a drive shaft 6 which extendslongitudinally through the cannula 4 and is connected externally to amotor 7.

The motor 7 can be actuated in both directions 8, 9, conveyance of fluidactually taking place merely in one direction of rotation.

The pump head 3 with the pump housing 5 is shown schematically in FIG. 2in longitudinal section and also the drive shaft 6. The latter ismounted rotatably at the front end of the pump head 3 in a bearing block10 by means of a bearing 11.

FIG. 2 shows the pump head in an expanded form, i.e. with enlargedradius relative to the representation of FIG. 1.

For introduction of the pump head 3 through a blood vessel 12 into theheart, the pump head 3 is compressed radially by making the shaft slackor by axial pressure on the shaft, i.e. is brought into the state of itslowest possible radial elongation.

If the pump head has arrived at the desired location, then the pumphousing can be drawn together axially by applying a tension in thedirection of the arrow 13 and consequently can be expanded radially, asindicated by the arrows 14, 15.

Compression and expansion of the housing by deformation of the housingis also conceivable, by means of using shape memory materials. Theresilient behaviour of shape memory materials at specific temperaturesis hereby exploited. Through the slots 16, 17 which extend in the axialdirection of the shaft 6, fluid, i.e. in the present case blood, canpass through the pump housing 5 towards the rotor 18 of the pump and canbe conveyed further through the latter, for example axially through thecannula 4. In FIG. 2, the inflow of the rotor has a radialconfiguration. In FIG. 2 a, an embodiment with axial inflow and outflowis represented schematically.

The rotor has a rotor blade carrier 19 and also rotor blades 20, 21, therotor blades 20, 21 being folded out during pump operation, i.e. in theexpanded state of the rotor.

The radius of the rotor during operation is coordinated to the internaldiameter of the pump housing in the expanded state thereof.

If the pump head is intended to be removed from the heart 1, then thepump operation is ceased and the rotor blades 20, 21 abut against therotor blade carrier 19 in order to reduce the radius of the rotor 18.This is advantageously assisted by rotation of the rotor 18 in thedirection of rotation opposite to the pump operation.

If the shaft 16 is then displaced towards the pump head 3 in the mannerof a Bowden cable, then the pump head again assumes its compressed formand can be removed through the blood vessel 12.

FIG. 3 shows in detail a plan view on the rotor 18 with the rotor bladecarrier 19 and the rotor blades 20, 21, these being represented in acontinuous shape in their first state, i.e. the compressed state of therotor. The rotor blades can also abut even more closely against therotor blade carrier 19 in the first state.

It is important that, when the pump operation and rotation of the rotor18 starts, in the direction of rotation 22 required for the conveyanceoperation, a fluid counterpressure is produced in the direction of thearrow 23 towards the rotor blades and these are bent by widening theradius of the rotor 18. If the pump is designed as a radial pump, thenthe fluid is displaced and hence conveyed radially outwards in thedirection of the arrow 24.

If the rotor blades 20, 21 are profiled in the axial direction, then thefluid can be conveyed also in the axial direction, as indicated in FIG.4 by the arrows 25, 26.

If the rotor is operated in a direction of rotation opposite to thedirection of rotation 22 required for the conveyance, then a fluidcounterpressure is produced on the rotor blades 20, 21, saidcounterpressure being opposite to the direction 23 and leading to therotor blades folding up against the rotor blade carrier 19 and to acorresponding reduction in the rotor diameter. In this state, the rotorcan be removed with a correspondingly compressed pump housing 5 out ofthe heart through the bloodstream.

By choice of the direction of rotation and the speed of rotation, thediameter of the rotor can hence be specifically changed, on the onehand, and, on the other hand, the conveyance power of the pump can beadjusted as desired.

FIG. 5 shows, by way of example, a rotor blade 21 with one side 27 whichis leading during the pump operation and also a trailing side 28, therotor blade having, along an interface 29, different properties on bothsides thereof. During operation, a fluid counterpressure acts on therotor blade in the direction of the arrow 23 and deforms the latter inthe second state in which the rotor is expanded. For this purpose, theleading side 27 must be able to be elongated to a specific degree andthe corresponding first material layer 30 has membrane properties forthis reason. This first material layer can involve for example rubber oran elastic plastic material which is elastically deformable up to apermanent elongation limit and resists further elongation thereafter asfar as possible.

On the trailing side 21, the second material layer 31 comprises acompression-resistant material which is configured for example to be sohard that it is deformed only minimally when forces are acting duringoperation so that bending of the rotor blade is produced exclusively viathe elongation of the first material layer 30.

However, a certain compressibility of the second material layer 31 canbe provided.

FIG. 6 shows a further example for configuration of a rotor blade inwhich notches 32 are provided in the second material layer 31, whichallow compression and bending of the trailing side until the notches 32are closed and the various webs formed between the notches 32 abutagainst each other in a form fit. In this state, further bending of therotor blade would be stopped.

The material of the first material layer 31 in this case can likewise bea hard plastic material from which parts are cut out or recessed in acasting or embossing process.

In this case also, the material of the first material layer 30 comprisesa material which can be elongated to a limited extent.

In FIG. 7, a rotor blade is represented in cross-section, the detailVIII in FIG. 8 being shown in more detail. The detail VIII thereby showsthe compression-resistant second material layer 31 a which, for itspart, has a multilayer construction in the manner of a sandwichstructure, the latter comprising tension—and/or compression-resistantexternal layers 33, 34, 35, 36 and also a volume layer 37. The externallayers 35, 36 can be reinforced for example with a woven material.

A very compression-resistant layer is hence formed on the trailing sideso that the deformability of the rotor blade is determined essentiallyby the ability of the leading side 27 to elongate.

In FIG. 9, a variant is represented in which a stop element 38 ismounted in the first layer 30, for example by means of a countersunkscrew 39, the stop element 38 protruding into an opening 40 of thesecond layer 31.

If the rotor blade 21 is deformed, then the opening 40 in the secondmaterial layer 31 will tend to be reduced and displaced until the edgesof the opening 40 abut against the stop element 38. The stop elementcomprises a hard material just like the second material layer 31 sothat, after abutment, no further compression is possible on the trailingside and the paddle blade is reinforced against further deformation.

FIG. 10 shows a helical rotor blade in which a series of shaped elements41, 42 on the trailing side of the blade are connected to each other,for example glued, or applied with a different joining method. In thecompressed state of the rotor, a spacing exists between the shapedelements respectively. During operation of the pump and after deployingthe blade, the shaped elements abut against each other and arereinforced as a continuous web which supports the flat parts of theblade acting as membrane and prevents further deformation. A pluralityof such rows of shaped elements can be disposed along the drive shaft 6axially and offset azimuthally.

A similar construction is shown in FIG. 11 where the web, forstrengthening the rotor blade, is formed by a winding comprising coils,for example comprising a plastic material, a spring wire or a hose. Theindividual coils respectively form one shaped element and are connectedindividually to the membrane-like surface of the rotor blade by gluing.During compression of the rotor, the gussets between the windings andopen close these during deployment of the blade. In order to stabilisethe winding, a continuous core is provided within the latter, said corebeing able to be flexible.

FIG. 12 shows the support of the rotor blade by a solid rail/connectingmember 45 in which a stop element is moveable in a limited fashion. Thestop element is connected to the rotor blade.

The rail/connecting member 45 can be configured, relative to the forcesand moments which act as expected, as bend-resistant andcompression-resistant component. As a result of the bending, smalladditional restoring forces are produced in this embodiment. Because ofthe low material thickness, regarded in absolute terms, few restoringforces are produced.

In FIG. 12, the stop element is located in the lower position. Bendingup to the bent situation would require high acting forces for thisposition due to the small length between connecting member take-up onthe shaft 6 and position of the guide pin in the rail/connecting member45.

The mentioned and described constructions of rotor blades are examplesof how, by means of different configuration of the various sides of therotor blades, a limited deformability during operation can be achievedby the fluid counterpressure.

During rotation of the rotor in a direction opposite to the operatingdirection, the deformation of the rotor blades is reversed and theseabut against the rotor, assume a first state and hence define thecompressed state of the rotor in which the latter can move easilythrough a narrow opening, for example a blood vessel or a tubularartificial access (valve).

Hence the invention allows, in a constructionally particularly simplemanner, production of a rotor which can be varied in its diameter forvarious applications, but particularly advantageously for the medicalfield.

1. Fluid pump, in particular liquid pump having a rotor (18) with atleast one rotor blade (20, 21) for conveying fluid, the rotor beingvariable with respect to its diameter between a first, compressed stateand a second expanded state, wherein the at least one rotor blade (20,21) is deformable between a first state which it assumes in thecompressed state of the rotor and a second state which it assumes in theexpanded state of the rotor by means of a fluid counterpressure (23)during a rotation of the rotor during pump operation, wherein the atleast one rotor blade (20, 21) has a leading (27) and a trailing side(28) in the direction of movement during the conveying operation,characterised in that said sides have different configurations in theform of different material properties and/ or constructional assembly atleast along a part of the distance between the radially outer tip of theblade and the radially inner end of the blade.
 2. Fluid pump accordingto claim 1, characterised in that the at least one rotor blade (20, 21)is elastically deformable by means of the fluid counterpressure (23). 3.Fluid pump according to claim 1, characterised in that the deformabilityof the at least one rotor blade (20, 21) is delimited by materialproperties and/or additional support elements on one side of the rotorblade.
 4. Fluid pump according to claim 3, characterised in that thedeformability of the at least one rotor blade (20, 21) is delimited insuch a manner that the deformation does not go beyond the shape in whichthe rotor produces the greatest possible fluid counterpressure.
 5. Fluidpump according to claim 4, characterised in that the leading side (27)of the at least one rotor blade (20, 21) comprises a first material andthe trailing side (28) comprises a second material which is differentfrom the first.
 6. Fluid pump according to claim 4, characterised inthat the first material is more ductile than the second material. 7.Fluid pump according to claim 6, characterised in that the firstmaterial has a permanent elongation limit.
 8. Fluid pump according toclaim 6, characterised in that fibres are embedded into the firstmaterial and are substantially more stretch-resistant than the firstmaterial.
 9. Fluid pump according to claim 5, characterised in that thesecond material is incompressible.
 10. Fluid pump according to one ofthe claims 5, characterised in that the second material is elasticallycompressible up to a compression limit.
 11. Fluid pump according toclaim 5, characterised in that a blade comprises a first layer ofmaterial on the leading side and a second layer of material on thetrailing side and that the second layer comprises trenches that allowfor compression of said second layer up to the extent that the trenchesare closed.
 12. Fluid pump according to claim 1, characterised in thatthe at least one rotor blade (20, 21) in its constructional assembleycomprises shaped elements (31, 41, 42, 43, 44) on the trailing side (28)or is connected to shaped elements which are at a spacing from eachother in the first state and abut against each other in the secondstate.
 13. Fluid pump according to claim 12, characterised in that theshaped elements (31, 41, 42, 43, 44) are separated from each other byslots (32) in the first state.
 14. Fluid pump according to claim 12,characterised in that the shaped elements (41, 42) are glued on oneside, in particular the trailing side, of a rotor blade or are appliedby another joining method.
 15. Fluid pump according to claim 12,characterised in that the shaped elements (43, 33) are formed byrespectively one coil of a winding.
 16. Fluid pump according to claim12, characterised in that the shaped elements (31, 41, 42, 43, 44) areembedded in a compressible material.
 17. Fluid pump according to claim1, characterised in that at least one stop element (38, 39) is mountedon one side of the at least one rotor blade which penetrates theinterface (29) between the leading side and the trailing side and ismoveable in a limited manner on the other side of the rotor blade in arecess.
 18. Fluid pump according to claim 1, characterised in that atleast one rotor blade comprises at least one winglet.
 19. Fluid pumpaccording to claim 18, characterised in that the at least one wingletprotrudes from the leading side of the blade.
 20. Fluid pump accordingto claim 18, characterised in that the at least one winglet protrudesfrom the trailing side of the blade.
 21. Fluid pump according to claim18, characterised in that at least one winglet is positioned at the tipof the blade.
 22. Fluid pump according to claim 17, characterised inthat at least one winglet is pivotable with regard to the blade. 23.Fluid pump according to claim 22, characterised in that at least onepivotable winglet is pivoted into its operating position by fluidpressure that is generated when the rotor is rotating.
 24. Method ofmaking a fluid pump according to claims 1, characterised in that formaking a blade, two layers of different materials are fixed to oneanother.
 25. Method of making a fluid pump according to claim 24,characterised in that the two layers are glued or soldered to oneanother.
 26. Method of making a fluid pump according to claim 1,characterised in that for making a blade, shaped bodies are fixed to oneside of a layer.
 27. Method for operating a fluid pump according toclaim 1, characterised in that the pump is started by rotation of therotor (18) in the operating direction and the rotor is expanded by thefluid counterpressure (23).
 28. Method for operating a fluid pumpaccording to claim 1, characterised in that in order to reduce the rotordiameter, the latter is actuated in the direction opposite to theoperating direction.
 29. Method for operating a fluid pump according toclaim 1, characterised in that the rotor (18) is actuated when the pumpis guided through an opening, in particular a blood vessel or a tubularartificial access, in the direction opposite to the operating direction.